In in-line varnishing (ink varnish, wet-in-wet) it is often required to keep adhesive strips, boxes for stamping and so on free from an application of varnish. In such cases the top rubber layer of the blanket (varnish blanket) clamped on a forme cylinder is incised in accordance with the position and size of the areas to be blanked out and is then removed. For accurate jobs the position of those parts of the varnish blanket required not to be varnished, i.e., required to be cut out, is so determined that a proof of the ink forme delivering the reference lines transmitted by the material being printed is applied by transfer to the dry varnish blanket. Cutting out the corresponding places in the press is time-consuming and increases set-up time. Removing the blanket after it has received the proof in order to cut it out parallel in time with the complete arrangement of the ink formes of the in-line press is, since the blanket has to be clamped again, also a time-consuming operation and above all cannot be dealt with beforehand.